The invention generally relates to pressure washers. In particular, the invention relates to a pressure washers having a duty cycle heater controller for supplying heated water.
Hot water pressure washers provide cleaning advantages over pressure washers that supply wash water at source temperature. Prior art pressure washers typically require the use of a thermostat control including a water temperature sensor for providing feedback to a controller to achieve temperature control. Unfortunately, such thermostat control systems typically provide relatively unstable temperature control. One of the reasons for such relatively unstable control is that the thermostat typically uses a temperature sensor to sense the temperature of the pipe in which the water flows. Thus, the temperature feedback provided to the thermostat-based control system lags the actual water temperature due to (1) the time it takes for the flowing water to heat or cool the pipe, (2) the time it takes the pipe to heat or cool the temperature sensor housing, and finally (3) the time it takes the housing to heat or cool the temperature sensor. Accordingly, adjustments to the burner used to heat the water are often poorly correlated with the desired output temperature, and result in undesirable overshoot and/or undershoot in the output water temperature.
For these reasons, an improved, highly accurate heater for hot water pressure washers is desired. The results obtained with such a pressure washer benefits from a more closely controlled water temperature range.
The invention meets the above needs and overcomes the deficiencies of the prior art by providing an improved temperature controller for a hot water pressure washer. This is accomplished by a less expensive, yet more accurate, calculated duty cycle burner controller system than the traditional thermostat control system. Advantageously, the present invention reduces costs by eliminating the need for a temperature sensor and thermostat, two typically costly items. Further, by eliminating the need to rely on a temperature sensor which introduces inherent delays, the improved temperature sensor provides a more constant output water temperature. Also, by controlling temperature by controlling the burner duty cycle, the burner xe2x80x9con timexe2x80x9d may be set at a fixed time interval with the off interval varied. Selecting an on time of suitable duration ensures a cleaner burn, which reduces burner soot and improves the reliability of the pressure washer while reducing pollution.
In one form, the invention comprises a pressure washer for use by an operator. A heat exchanger has a water input adapted to connect to a water source and has a water output providing discharge. A cycle timer is responsive to the flow of water flow through the heat exchanger. A burner in thermodynamic communication with the heat exchanger applies heat to the heat exchanger and to the water in the heat exchanger. The burner has a fuel input connecting a fuel source to the burner. A fuel switch is responsive to the cycle timer. The fuel switch selectively allows fuel from the fuel source to be supplied to the burner via the fuel input, whereby the cycle timer controls the duty cycle of the fuel switch and thereby controls temperature of the water in the heat exchanger.
In another form, the invention comprises a pressure washer for use by an operator. A heat exchanger has a water input adapted to connect to a water source and has a water output providing discharge water. A water pump supples water to the heat exchanger. A temperature selector is responsive to operator. A burner in thermodynamic communication with the heat exchanger applies heat to the heat exchanger and the water in the heat exchanger. The burner has a fuel input connecting a fuel source to the burner. A fuel switch selectively allows fuel from the fuel source to be supplied to the burner via the fuel input. A duty cycle timer has a uniform duty cycle and is energized when water flows through the heat exchanger. The duty cycle timer is responsive to the temperature selection switch to vary its duty cycle as a function of the operator input provided to the temperature selector. The duty cycle timer controls the fuel switch to supply fuel to the burner according to the duty cycle of the duty cycle timer whereby the duty cycle timer controls the burner and thereby controls temperature of the water in the heat exchanger.
In yet another form, the invention comprises a pressure washer for use by an operator, as follows. A heat exchanger has a water input adapted to connect to a water source and has a water output providing discharge water. A water pump supplies water to the heat exchanger. A temperature selector is responsive to operator input. A burner in thermodynamic communication with the heat exchanger applies heat to the heat exchanger and the water in the heat exchanger. The burner has a fuel input connecting a fuel source to the burner. A fuel switch selectively allows fuel from the fuel source to be supplied to the burner via the fuel input. A processor is responsive to the temperature selection switch to vary the duty cycle of the fuel switch as a function of the operator input provided to the temperature selector.
In another form, the invention is a method of providing pressurized, heated water comprising the steps of:
supplying water at a flow rate through a heat exchanger having a water input adapted to connect to a water source and having a water output providing discharge water; and
applying heat to the heat exchanger at a duty cycle which is a function of the flow rate of the water and which is a function of a desired temperature of the discharge water.
Other objects and features will be in part apparent and in part pointed out hereinafter.